Fixture and system for treating test pieces on a rapid cycle leak detection apparatus

ABSTRACT

The test piece is clamped to the base of the fixture in such a way that one side of said test piece is exposed to a vacuum created by the leak detection apparatus and the other side of said test piece is exposed to a test-gas receiving chamber. The act of clamping the test piece to the base of the fixture causes the test-gas receiving chamber to be formed and simultaneously causes a test gas such as helium to fill said chamber to a predetermined pressure. After the test piece has been clamped into testing position and the test gas has filled the test-gas chamber, a mechanism is activated which admits air to said chamber at higher pressure than said test gas therein and which simultaneously activates the leak detection apparatus. Before the leak detection apparatus connects said one side of the test piece to vacuum, the high-pressure air is cut off and said test-gas chamber contains only a small quantity of high-pressure air and is not open to the source of high-pressure air. Thus, if a particular test piece has a leak, the quantity of high-pressure air passing through the leak will be insufficient to damage the delicate mechanism of the leak detection apparatus.

United States Patent [191 Briggs et al.

FIXTURE AND SYSTEM FOR TREATING TEST PIECES ON A RAPID CYCLE LEAKDETECTION APPARATUS Inventors: Walton E. Briggs, Lynnfield; Paul R.

Fruzutti, North Easton, both of Mass.

Assignee: Varian Associates, Palo Alto, Calif. Filed: July 2, 1971 App].No.: 159,234

Primary Examiner- Louis J. Capozi A we Stev e 2199192991 0" He [45] Aug.14 1973 [57] ABSTRACT The test piece is clamped to the base of thefixture in such a way that one side of said test piece is exposed to avacuum created by the leak detection apparatus and the other side ofsaid test piece is exposed to a testgas receiving chamber. The act ofclamping the test piece to the base of the fixture causes the test-gasreceiving chamber to be formed and simultaneously causes a test gas suchas helium to fill said chamber to a predetermined pressure. After thetest piece has been clamped into testing position and the test gas hasfilled the test-gas chamber, a mechanism is activated which admits airto said chamber at higher pressure than said test gas therein and whichsimultaneously activates the leak detection apparatus. Before the leakdetection apparatus connects said one side of the test piece to vacuum,the high-pressure air is cut off and said test-gas chamber contains onlya small quantity of highpressure air and is not open to the source ofhighpressure air. Thus, if a particular test piece has a" leak, thequantity of high-pressure air passing through the leak will beinsufficient to damage the delicate mechanism of the leak detectionapparatus.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention isa further development in the art of measurements, and particularly inthe technique for leak detection employing a high pressure differential.

2. Description of the Prior Art Use of a test gas under pressure fordetecting leaks is well known. However, prior art techniques havegenerally been slow and unquantitative. In one approach, leaks aredetected by observing gas bubbles rising in a container of liquid suchas water. A mechanical device for detecting leaks by this method isdisclosed in US. Pat. No. 3,323,351. An improved quantitative leakdetector is disclosed in US. Pat. No. 3,385,102 wherein the leaking testgas is detected by a very sensitive mass spectrometer. However, it hasbeen impracticable heretofore to use a test gas under pressure forquantitative measurement of leakage by sensitive gas analysisinstruments because rupture of the test piece would generally cause thehigh-pressure test gas to damage said instruments.

SUMMARY OF THE INVENTION This invention teaches an apparatus andtechnique for using a test gas at high pressure in conjunction with aleak detection apparatus which incorporates a finevacuum gas analysisinstrument such as a mass spectrometer for rapid and quantitativelymeasured leak 'detection. It is a feature of this invention that thetest gas may be used at a high pressure without danger to the sensitiveinstruments in the leak detection apparatus. It is another feature ofthe invention to provide a substantially automatic testing apparatus. Itis also a feature of the invention to provide a testing apparatus whichcan be conveniently and quickly loaded and unloaded by the operator.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front view of atwo-station fixture system which embodies the features of thisinvention.

FIG. 2 is a side view taken from the right of FIG. 1 but showing thelower part in cross section.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a pair of fixturesl and 2 mounted on a common supporting structure including a supportplate 3, block 4, U-shaped brackets and a supporting rod 6. The block 4is secured to the plate 3. The brackets 5 and the rod 6 are secured tothe block 4. Each of the fixtures can be operated singly or as a memberof a plurality of such fixtures. Fixture I is shown with the handle 8 ofa toggle clamping device in the upward position, while fixture 2 isshown with an identical handle in the downward position. In FIG. 1, atest piece 10 is shown about to be'lowered manually by the operator intotest position in fixture 1, and a test piece has been clamped into testposition in fixture 2. The test piece 10 could be for example the metaltop of a beverage container such as a beer can.

The support plate 3 and the support rod 6 are secured to a base member11. As shown in FIG. 2, base I I is mounted by screws 12 (only oneshown) to a valve housing 13 of a rapid-cycle leak detection apparatus.For example, the housing 13 corresponds to the housing for valve spools50 and in US. Pat. No. 3,385,102.

The toggle clamp for each fixture includes the handle 8 which is mountedon a fixed pivot 16 supported from:

the bracket 5. The handle 8 carries a travelling pivot 17 whichpivotally supports an arm 18. Arm 18 is pivotally.

connected at 19 to avertically movable clamping rod 20. Rod 20 ismounted in a sleeve bearing 21 secured; to the bottom of bracket 5. Thebottom of rod 20' ceives acylindrical insert 30, and each of the inserts30 receives a cylindrical adaptor 31. A test piece supporting andlocating disk 32 of circular shape is received in each adaptor 31.O-rings 33 and 34 of'suitable material;

such as rubberseal the bottom of insert 30 against the top of valvehousing 13. Similarly, O-rings 35 and 36 seal the adaptor 31 in theinsert 30. An O-ring 37 is positioned over the outer portion of adaptor31. As shown in FIG. 2, the lower periphery of the test piece 10 issealed against O-ring 37 when the test piece is clamped in testingposition. The test piece 10 shown in FIG. 2 has a conventional pull-tab38. The locating disk 32 is mounted on springs 39. Only one such springis shown but it will be understood that three or more of the springs areuniformly placed around a circle concentric with the axis of disk 32.One function of springs 39 is to raise the test piece 10 for easygrasping by the operator when handle 8 is raised. The travel of springs39 is limited so they merely raise the disk 32 but do not eject it fromthe adaptor 311.

Disk 32 includes an upwardly extending annular rim 40 which engages theundersurface of the test piece. The springs 39 also serve to allow thetest piece 10 to be easily centered on the rim 40, because when the disk32 is in its raised position the test piece will not be held awayfromthe disk 32 by abutment of the test piece 10 against the O-ring 37.When the handle 8 is moved to its lower position, as in FIG. 2, theupper surface of the test piece 10 will be sealed against sealing ring25 and the lower surface will be sealed against O-ring 37. Thus agas-receiving chamber 41 will be formed between the dome cover 24 andthe upper surface of the test piece 10, and an evacuation chamber 42will be formed between the lower side of the test piece and the locatingdisk 32. Each of the members 30, 31 and 32 has a cen-.

tral bore therethrough forming an evacuation passage 43. Passage 43 islocated so that it communicates with the test port in the vacuumdetection apparatus. More specifically, the evacuation passage 43 foreach of the fixtures l and 2 is positioned in aligned communicationabove the test port 40 in US. Pat. No. 3,385,102. Rim 40 on the locatingdisk 32 has a plurality of apertures 44 to permit leak checking of theouter part of test piece 10.

A conventional spool valve 50 is attached to the block 4 for each of thefixtures 1 and 2 respectively. Valve 50 has an upper port 51 connectedto a T-fitting 52 which supports a pressure gauge 53. Valve 50 has alower port 54 which is connected by a flexible line 55 to the gasfitting 26 on the dome cover 24. Valve 50 also has an exhaust port 56which opens to the atmosphere. The valve 50 has a valve spool 57 whichis normally biased to the left by spring 58. When the handle 8 is movedto its downward position it abuts the left end of spool 57 and forcesthe spool to the position shown in FIG. 2, in which position port 51 isconnected to port 54. When the handle 8 is moved to its upper positionit moves away from the left end of spool 57 and the spool is permittedto move to the left so that port 51 is isolated and port 54 is connectedto the exhaust port 56.

A gas conduit 62 is connected from T-fitting 52 to a conventionalshuttle valve 63. The shuttle valve 63 has an inlet fitting 64 connectedto a source of test gas 65. The valve 63 also has an inlet fitting 66connected to a spool valve 67. As indicated schematically in dottedlines, the shuttle valve 63 has a valve ball 68 which in its upperposition closes against a seat 69 and in its lower position closesagainst a seat 70. The ball 68 is moved to its upper position when airunder higher pressure than the test gas is admitted to inlet 66.

The spool valve 67 is substantially the same as spool valve 50, exceptthat its exhaust port is closed by a plug 74. The valve 67 has an inletport 75 connected to a high pressure air line 76, and an outlet port 77connected to the inlet fitting 66 of valve 63. A valve spool 73 isbiased to the left by spring 78 and is moved to the right by actuatinglever 79 pivoted at 80. When the spool 73 is held to the right, as inFIG. 2, the inlet port 75 is connected to the outlet port 77. When lever79 is permitted to move to the left, as will be hereinafter described inmore detail, spring 78 moves spool 73 to the left to isolate the inletport 75 so that high pressure air does not reach the outlet port 77.Valve 67 is mounted on a bracket 81 which is secured to a frame member82 that forms part of the leak detector apparatus.

The leak detector apparatus comprises a cylinder 83 containing a piston84 which drives an actuating rod 85 connected to the valve spool (notshown) in the valve housing 13. The cylinder 83 corresponds to thecylinders 60 and 160 in U.S. Pat. No. 3,385,102. Similarly, theactuating rod 85 corresponds to rods 62 and 162 in that patent, and thevalve spool (not shown) corresponds to the valve spools 50 and 150 inthat patent. Actuating rod 85 carries an abutment collar 86 which in itssolid line position holds valve lever 79 in the closed position. It willbe understood that a separate cylinder 83 together with its piston 84,actuating rod 85 and the associated valve spool is provided for each ofthe fixtures l and 2. Similarly, duplicate valves 50, 63, 67 and relatedconnections are provided for each of the fixtures.

The piston 84 is actuated by a source of compressed air 88 through anautomatic valve shown schematically at 89 of a conventional type foradmitting compressed air first to the right and then to the left ofpiston 84 in timed sequence as explained in U.S. Pat. No. 3,385,102. Thecompressed air source 88 is also connected to the inlet port 75 of valve67 through the line 76 which is connected to cylinder 83 at the right ofpiston 84. An operating lever 92 is shown in FIG. 1 in its off position.The lever 92 is movable to the right as shown in dotted lines to causeactuation of valve 89 for fixture 2 and to the left for actuation of thecorresponding valve for fixture 1. As shown schematically in FIG. 2, thelever 92 is connected to the valve 89 through a suitable linkage 93including a timer 94.

OPERATION The operating procedure is to actuate the fixtures l and 2 insequence as will now be described. With the handle 8 on one of thefixtures in its raised position, a test piece 10 is manually positionedby the operator on the locating disk 32 in the position shown in FIG. 2,except that at that time the locating disk will be raised slightly bysprings 39. Then handle 8 is lowered to clamp the test piece 10 in placeas shown in FIG. 2. When the handle 8 is lowered, it will force thevalve spool 57 to the right and thereby connect the source of test gas65 through valves 63 and 50 to the gasreceiving chamber 41 under theclamping dome 24. At the time the handle 8 is lowered, the valve 67 doesnot pass compressed air to its outlet 77 because valve 89 is positionedto prevent admitting compressed air to the inlet of valve 67, so thatthe valve ball 68 will be held by gravity and by the test gas pressureagainst its lower seat 70. After the handle 8 is moved to its downwardposition, that fixture, for example fixture 2 in the drawings, is readyfor test. The test is accomplished by moving lever 92 to the right asshown dotted in FIG. 1. This causes valve 89 to admit compressed air tothe right of piston 84 to initiate the testing sequences explained indetail in U.S. Pat. No. 3,385,102. The movement of lever 92simultaneously connects the source of compressed air 88 to the inletport of valve 67 through cylinder 83 and line 76. At this instant, thevalve 67 is in its open position so that compressed air is admittedthrough valve 67, valve 63 and'valve 50 into the gas receiving chamber41. As the compressed air moves through shuttle valve 63, it forces ball68 against the upper seat 69, thus preventing compressed air fromreaching the source of test gas 65. As the actuating rod moves to theleft out of cylinder 83, the abutment collar 86 will move away from thevalve lever 79 toward its dotted line position. As a result, the spring78 will move the valve spool 73 to the left to close the inlet passage75 so that the source of compressed air 88 will be cut off, leaving justa small charge of compressed air in the gas-receiving chamber 41 and thecommunicating lines 55 and 62 between the chamber 41 and valve 67. Timer94 is set so that after a test is completed valve 89 is moved to admitcompressed air to the left of piston 84 to return the rod 85 to itsoriginal position, as explained in more detail in U.S. Pat. No.3,385,102. When valve 89 is moved in this manner, the air source 88 isclosed off from valve 67 so compressed air will not blast out when theoperator raises handle 8 for the reloading procedure, and so that testgas can pass through the shuttle valve 63 when the operator lowershandle 8 for the next test. When valve 89 closes the source ofcompressed air 88 from the right of piston 84, it also vents the rightside of the piston 84 to atmosphere as is customary in cylinder-pistonoperation.

As soon as the lever 92 has been moved to the right to start the testingsequence for fixture 2, the operator loads fixture l and lowers thehandle 8 for that fixture. As soon as the test is completed for fixture2 and piston 84 is returned to the right-hand position, the operatormoves the lever 92 toward the now loaded fixture 1. While the test isbeing conducted for fixture l, the operator unloads and reloads fixture2; and this sequence of operation is continued throughout the testprogram. When the operator raises handle 8 to unload fixture 2, thehandle 8 will move away from spool 57 and spring 58 will move the spool57 to the left to isolate the inlet port 51 and conserve the test gassupply. At the same time, the gas chamber 41 will be vented toatmosphere through port 56 in order to vent the test gas away from thetest area so that the test gas will not become trapped under the nexttest piece.

The test gas in source 65 is preferably helium and is preferably under apressure of between one and three pounds per square inch aboveatmospheric pressure. The source 88 is described as a source ofcompressed air. Obviously other inexpensive compressed gas could beused. In any event the source of compressed gas 88 is preferably at apressure of forty-five pounds per square inch above atmosphericpressure.

The features of this invention which I claim are as follows:

l. Leak detecting apparatus comprising means for supporting a test piecewith one side thereof adapted to be exposed to a vacuum leak detector, acover member adapted to sealingly engage the other side of said testpiece to form a gas-receiving chamber between said cover member and saidtest piece, clamping means to force said cover member against said testpiece, a test gas supply line, first valve means connected in seriesbetween said test gas supply line and said gas-receiving chamber, a gaspressure supply line, and second valve means connected in series betweensaid gas pressure supply line and said gas-receiving chamber.

2. Leak detecting apparatus as claimed in claim 1 further comprisingactuating means between said clamping means and said first valve meansto cause said first valve means to open when said clamping means causessaid cover member to sealingly engage the test piece.

3. Leak detecting apparatus as claimed in claim 1 fur ther comprising ashuttle valve connected between said test gas supply line and said firstand second valve means whereby, when said second valve means is open,gas from said gas pressure supply line is prevented from reaching saidtest gas supply line.

4. Leak detecting apparatus as claimed in claim 1 in which said leakdetector comprises third valve means for connecting said one side ofsaid test piece to the leak detector, means for moving said third valvemeans to connect said one side of said test piece to the leak detector,and actuating means between said moving means and said second valvemeans to cause said second valve means to close before said one side ofsaid test piece is exposed to the leak detector; whereby, if said testpiece ruptures, said gas pressure supply line will not be connected tosaid gas-receiving chamber.

5. Leak detecting apparatus as claimed in claim 1 in which said firstvalve means has an inlet port connected to said test gas supply line, anoutlet port connected to said gas-receiving chamber, and a vent portconnected to said outlet port when said outlet port is disconnected fromsaid inlet port, said vent port being positioned away from the locationof said gas-receiving chamber.

6. Leak detecting apparatus comprising a test piece supporting memberfor supporting a test piece with one side of the test piece adapted tobe exposed to a vacuum leak detector, a cover member adapted tosealingly engage the other side of said test piece to form agas-receiving chamber between the cover member and the test piece, meansfor forcing said cover member against said test piece, said supportingmember being slidingly received in an adaptor member, said adaptormember having a sealing surface positioned to engage said one side ofsaid test piece outwardly of said supporting member, and spring meansurging said supporting member away from said adaptor member in thedirection of said cover member.

7. Leak detecting apparatus as claimed in claim 6 in which saidsupporting member has an annular rim portion projecting toward saidcover member, said rim portion having a hole therethrough, and saidsealing surface being an annular surface surrounding said rim portion.

8. Leak detecting apparatus comprising means for supporting a test piecewith one side adapted to be exposed to a vacuum leak detector and sealedfrom the ambient atmosphere, a cover member adapted to sealingly engagethe other side of said test piece to form a gas-receiving chamberbetween the cover member and the test piece, a supply line for gas underpressure, a first valve connected in series between said supply line andsaid gas-receiving chamber, a second valve between said one side of thetest piece and the leak detector, and operating means interconnectingsaid first and second valves for causing said first valve to be closedwhen said second valve is open.

9. Leak detecting apparatus comprising means for supporting a test piecewith one side thereof adapted to be exposed to a vacuum leak detector, acover member adapted to sealingly engage the other side of said testpiece to form agas-receiving chamber between said cover member and saidtest piece, clamping means to force said cover member against said testpiece, a test gas supply line, valve means connected in series betweensaid test gas supply line and said gas-receiving chamber, and actuatingmeans between said clamping means and said valve means and separatedfrom the test piece to cause said valve means to open when said clampingmeans causes said cover member to sealingly engage the test piece.

10. The method of testing for leaks in a test piece comprising the stepsof positioning the test piece in a test apparatus so that one side ofthe test piece is adapted to be exposed to a leak detector, forming agas-receiving chamber on the other side of the test piece, connecting asource of fiuid under pressure to said gas-receiving chamber, and thendisconnecting said fluid pressure source from said gas-receiving chamberwhile trapping in said chamber a charge of gas under pressure from saidsource, whereby the leak de tector will be protected from the fullsupply of fluid under pressure which could otherwise pass through a holein the test piece and reach the leak detector.

1. Leak detecting apparatus comprising means for supporting a test piecewith one side thereof adapted to be exposed to a vacuum leak detector, acover member adapted to sealingly engage the other side of said testpiece to form a gas-receiving chamber between said cover member and saidtest piece, clamping means to force said cover member against said testpiece, a test gas supply line, first valve means connected in seriesbetween said test gas supply line and said gas-receiving chamber, a gaspressure supply line, and second valve means connected in series betweensaid gas pressure supply line and said gas-receiving chamber.
 2. Leakdetecting apparatus as claimed in claim 1 further comprising actuatingmeans between said clamping means and said first valve means to causesaid first valve means to open when said clamping means causes saidcover member to sealingly engage the test piece.
 3. Leak detectingapparatus as claimed in claim 1 further comprising a shuttle valveconnected between said test gas supply line and said first and secondvalve means whereby, when said second valve means is open, gas from saidgas pressure supply line is prevented from reaching said test gas supplyline.
 4. Leak detecting apparatus as claimed in claim 1 in which saidleak detector comprises third valve means for connecting said one sideof said test piece to the leak detector, means for moving said thirdvalve means to connect said one side of said test piece to the leakdetector, and actuating means between said moving means and said secondvalve means to cause said second valve means to close before said oneside of said test piece is exposed to the leak detector; whereby, ifsaid test piece ruptures, said gas pressure supply line will not beconnected to said gas-receiving chamber.
 5. Leak detecting apparatus asclaimed in claim 1 in which said first valve means has an inlet portconnected to said test gas supply line, an outlet port connected to saidgas-receiving chamber, and a vent port connected to said outlet portwhen said outlet port is disconnected from said inlet port, said ventport being positioned away from the location of said gas-receivingchamber.
 6. Leak detecting apparatus comprising a test piece supportingmember for supporting a test piece with one side of the test pieceadapted to be exposed to a vacuum leak detector, a cover member adaptedto sealingly engage the other side of said test piece to form agas-receiving chamber between the cover member and the test piece, meansfor forcing said cover member against said test piece, said supportingmember being slidingly received in an adaptor member, said adaptormember having a sealing surface positioned to engage said one side ofsaid test piece outwardly of said supporting member, and spring meansurging said supporting member away from said adaptor member in thedirection of said cover member.
 7. Leak detecting apparatus as claimedin claim 6 in which said supporting member has an annular rim portionprojecting toward said cover member, said rim portion having a holetherethrough, and said sealing surface being an annular surfacesurrounding said rim portion.
 8. Leak detecting apparatus comprisingmeans for supporting a test piece with one side adapted to be exposed toa vacuum leak detector and sealed from the ambient atmosphere, a covermember adapted to seAlingly engage the other side of said test piece toform a gas-receiving chamber between the cover member and the testpiece, a supply line for gas under pressure, a first valve connected inseries between said supply line and said gas-receiving chamber, a secondvalve between said one side of the test piece and the leak detector, andoperating means interconnecting said first and second valves for causingsaid first valve to be closed when said second valve is open.
 9. Leakdetecting apparatus comprising means for supporting a test piece withone side thereof adapted to be exposed to a vacuum leak detector, acover member adapted to sealingly engage the other side of said testpiece to form a gas-receiving chamber between said cover member and saidtest piece, clamping means to force said cover member against said testpiece, a test gas supply line, valve means connected in series betweensaid test gas supply line and said gas-receiving chamber, and actuatingmeans between said clamping means and said valve means and separatedfrom the test piece to cause said valve means to open when said clampingmeans causes said cover member to sealingly engage the test piece. 10.The method of testing for leaks in a test piece comprising the steps ofpositioning the test piece in a test apparatus so that one side of thetest piece is adapted to be exposed to a leak detector, forming agas-receiving chamber on the other side of the test piece, connecting asource of fluid under pressure to said gas-receiving chamber, and thendisconnecting said fluid pressure source from said gas-receiving chamberwhile trapping in said chamber a charge of gas under pressure from saidsource, whereby the leak detector will be protected from the full supplyof fluid under pressure which could otherwise pass through a hole in thetest piece and reach the leak detector.